Be aware of the drugs that require slow intravenous administration

Physicians often rely on pharmacists to relay important information regarding the IV administration of particular medications....
Abdelwahab Ward, BS Pharm, PharmD

Introduction ― The speed at which intravenous (IV) medications can be administered is often overlooked and can have devastating consequences. The drug package inserts contain information on administration, but these are frequently unavailable to anesthesiologists and the information included is not always appropriate for anesthetized patients. Physicians often rely on pharmacists to relay important information regarding the IV administration of particular medications. However, physicians frequently prepare medications for administration without pharmacy intervention. The purpose of this topic is to review common medications that need to be administered slowly or that have other special considerations. The following medications must be given slowly when they are administered intravenously: Phenytoin, vancomycin, potassium chloride, clindamycin, furosemide, gentamicin, and oxytocin...

MEDICATIONS

Phenytoin. Phenytoin is a neurologic and cardiac depressant and is one of the most dangerous medications we administer intraoperatively. For status epilepticus, the maximum rate of IV administration is 50 mg/min (for children, 1 to 3 mg/kg/min up to a max of 50 mg/min). Because we generally give the medication prophylactically in the operating room, it is recommended to administer phenytoin much more slowly in anesthetized patients (e.g., max. 10 to 20 mg/min).  

          Elderly patients and patients with cardiovascular disease should also receive the medication more slowly. If phenytoin is given rapidly IV, asystole and cardiovascular collapse is possible, but more commonly hypotension, bradycardia, and cardiac dysrhythmias are seen. These effects may be related to the diluent (propylene glycol) and may be minimized by using fosphenytoin. The dose must also be adjusted in those with hypoalbuminemia and liver disease. It is advised that the medication be diluted in normal saline to a final concentration of 1 to 10 mg/mL and be administered with an infusion pump. Extravasation of this medication can cause severe soft tissue injury, and it is therefore recommended to inject phenytoin into a large vein through a large-gauge IV catheter. Be sure to flush the line before and after administration with normal saline. This medication may be piggybacked, but there is a high potential for precipitation in the presence of other medications, so a 0.22-µm filter should be used. 

  • REMEMBER..
    Do not accept information from the neurosurgeons as to the appropriate rate of phenytoin infusion — know the limiting rate yourself and personally insure it is not being exceeded. If the surgeons insist they cannot continue on with the case until the infusion is complete, then advise them they may have to adjust their expectations about how rapidly the case will proceed, but do not speed up the rate of the infusion.

Gentamicin has a small therapeutic window, which can make dosing challenging. Dosing adjustments in situations of renal impairment are particularly important. Aminoglycosides in general are associated with both nephrotoxicity and ototoxicity. It is thought that toxicity is related to the dose given and the duration of therapy. There have been reports of hypotension after administration of an aminoglycoside, and it is therefore recommended that gentamicin be diluted and administered slowly. Gentamicin can potentiate neuromuscular blockade.

Vancomycin. Administration of vancomycin should be no faster than 10 mg/min and should be administered with the use of an infusion pump. “Red man” syndrome (erythematous rash on face and body) may occur, and if so, the infusion rate should be reduced. Rapid IV infusion has been reported to cause hypotension and, rarely, cardiac arrest. Vancomycin may cause soft tissue injury if it extravasates. When possible, a large-gauge IV catheter or central line should be used for administration.

Potassium. Potassium may precipitate cardiac arrhythmias if serum concentrations increase too rapidly. In general, the maximum speed of administration is 40 mEq/hr. The patient should have electrocardiogram (EKG) monitoring in place before administration. This medication causes venous irritation, so infusion via large IV catheters is preferred. If it is not prepackaged, potassium must be diluted.

Clindamycin should be diluted before administration to a concentration of no more than 18 mg/mL. Do not “push” clindamycin intravenously, because it can cause profound hypotension. Infuse over 10 to 60 minutes at a rate no greater than 30 mg/min. This medication can cause thrombophlebitis at the injection site.

Furosemide (Lasix). Lasix should also be administered slowly over 1 to 2 minutes. Administer no faster than 4 mg/min if large doses are to be given. There have been reports of acute hypotension and sudden cardiac arrest after IV administration. Ototoxicity has been associated with rapid IV infusion. Renal impairment, concurrent administration of other ototoxic medications, and excessive doses increase the risk of ototoxicity.

REFERENCES

Abdelwahab Ward, BS Pharm, PharmD